(1) Field of the Invention
The present invention relates to beam lead bonding apparatus and, more particularly, to a beam lead bonding apparatus employing a compressible pad and protective layer between the substrate being bonded and a base support.
(2) Background Art
In the electrical art it is often necessary, in the manufacture of printed wiring board assemblies utilizing integrated circuits, to connect the integrated circuit substrates to conductors formed on the printed wiring board through the use of strap like connectors commonly called beam leads. In this regard, it is desirable initially to attach beam leads to an integrated circuit substrate. The beam leads may then be attached to the printed wiring board conductors to establish connection to the integrated circuit to other integrated circuits thereby forming an electronic assembly. In the past such device beam leads were individually attached to the integrated circuit substrate using a time consuming laborious manual process.
Improvements have been made to automate the bonding process as is illustrated by U.S. Pat. No. 3,700,156 issued Oct. 24, 1972 to Hermanns which teaches an apparatus including an element for bonding beam leaded devices to a substrate by successively contacting and bonding each of a plurality of beam leads projecting from around periphery of a beam leaded device. The bonding head is moved in a complex wobbling fashion to individually and successively automatically bond each lead to the substrate which reduced time and labor. Additionally, the wobble bonder of Hermanns allowed for variations in beam lead thicknesses.
While operating generally satisfactorily, the wobbling action has been achieved only through the use of a complex mechanical arrangement which is expensive to manufacture. Additionally, the sequential bonding of the beam leads has frequently resulted in tensile stresses being set up within the leads thereby contributing to early device failures.
Another arrangement for bonding leads of a device equipped with beam leads to substrates is taught by U.S. Pat. Nos. 3,442,432 and 3,475,814 issued May 6, 1969 and Nov. 4, 1969, respectively, to Santagini. Santagini teaches a method and apparatus for the simultaneous bonding of device beam leads to a substrate utilizing a bonding tool which applies pressure and bonding energy simultaneously to all of the leads being bonded. A moveable ball is located within a bore formed in a base which initially supports the substrate. The ball is raised to engage, lift, and pivotly support the substrate above the base surface in contact with a plurality of beam leads which are positioned between the substrate and a bonding head. The substrate pivots about the moveable ball to compensate for unequal beam lead thicknesses while at the same time permitting the simultaneous bonding of all the beam leads thereby preventing the creation of axial stresses within the leads.
Such an arrangement, while operating generally satisfactorily, has been found to cause substrate fracture due to the concentration of force at a central point of the substrate.
Additionally, the above art, while related to the subject invention, addresses the problem of attaching beam lead equipped devices to substrates and not the problem of attaching beam leads to integrated circuit substrates.
Accordingly, it is a object of the present invention to provide a new and useful beam lead bonding apparatus that provides the benefit of simultaneously bonding a plurality of beam leads of varying thicknesses to an integrated substrate while preventing fracture of the substrate to a greater degree than found in previously utilized designs.